Gain and volume control - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd September 2003, 07:13 PM   #1
diyAudio Member
 
Hybrid fourdoor's Avatar
 
Join Date: May 2003
Location: Ft. Worth, TX
Question Gain and volume control

I see almost everyone in most cases does volume control by putting a pot inline with R(in) or replaceing it completely. But this seems to cause problems for some because that changes the input resistance.

So I have a question. Can you use a pot to adjust the gain by increaseing Ri. Since gain is determined by Rf/Ri right? Rf=20K and Ri=1K equals a gain of 20? So if you added 9K or resistance to Ri the gain is now 2 right? But the input resistance stays at 47K or whatever you set it at. Plus less stuff in the input path!!!

Does this cause any problems such as oscilating or other stability problems? Plus wouldn't the noise be lower, the less gain you have?

Attached is a drawning of what I mean. Hope I'm not irratatiing you with all my crazy ideas!

I left Ri in there as 1K, that way at zero resistance on the pot you still have some resistance...sorta as a safety thing. And I used a 20K pot purely out of ease of numbers, I don't think there are 20K pots.
Attached Images
File Type: gif gainclone.gif (1.9 KB, 758 views)
  Reply With Quote
Old 23rd September 2003, 08:40 PM   #2
diyAudio Member
 
JOE DIRT®'s Avatar
 
Join Date: Apr 2003
Location: Brantford, ON
there is nothing wrong with doing it that way but you will need a resistor from the pot to ground or else with the wiper advanced all the way your source will see a short


misread it...your input is not on the pot....your feed back will change for sure
  Reply With Quote
Old 23rd September 2003, 08:54 PM   #3
diyAudio Member
 
Join Date: May 2002
Location: Plano , TX
Send a message via AIM to jewilson
Default volume adjustment

By adding a pot there, you change the open loop gain of the circuit when adjusting. When you change the gain, you will also be changing the phase response. If amp is not unit gain stable, it will oscillate. As you change gain, the offset can vary. Running even short wires to the pot will add some capacitance.

That why you don't see pot in the circuit there.
__________________
Jim W.
  Reply With Quote
Old 23rd September 2003, 08:55 PM   #4
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Hi,

Nice bit of lateral thinking, but unfortunately there may be stability problems.
The chip amp is just an op-amp. These are stable for a particular range of gain. If you reduce the gain too much it will probably hoot.
You also cannot reduce the signal to zero.

Cheers,
  Reply With Quote
Old 23rd September 2003, 09:39 PM   #5
Account Disabled
 
Join Date: Apr 2003
Location: US
Default Re: volume adjustment

Quote:
Originally posted by jewilson
By adding a pot there, you change the open loop gain of the circuit when adjusting. [/B]

how do you change the open loop gain? close loop gain? maybe but open loop gain?

I think it could work (and likely works) as a lot of power amps are unity stable - all bridgeable amps are unity stable for example. It is just I cannot see any benefit for doing this.
  Reply With Quote
Old 23rd September 2003, 11:10 PM   #6
diyAudio Member
 
Hybrid fourdoor's Avatar
 
Join Date: May 2003
Location: Ft. Worth, TX
The reason I was thinking this was because it would keep the input impedence at a constant, plus you wouldn't have a cheap potetiometer in the signal path. Although I admit my knowledge is low, but someone had already taken a name indicating that ( )

I added that 1K resistor that way even if you put the pot all the way to no resistance it still would have 1K. Actaully thus setting the maximum gain level, because turning the pot would lower level...just backwards compared to normal.

But I guess as long as you put the pot AND a input restistor you would have pretty good design that is time proven huh? h well, just spreading the ideas around, you never know some guy might see this idea and before we know all amps sold under Harmon International are using the technic!
  Reply With Quote
Old 23rd September 2003, 11:14 PM   #7
Kay is offline Kay  Germany
diyAudio Member
 
Join Date: Nov 2001
Location: Emden
>If you reduce the gain too much it will probably hoot.
>You also cannot reduce the signal to zero.

Try this
Attached Images
File Type: gif bild1.gif (2.4 KB, 648 views)
__________________
best regards
Kay
  Reply With Quote
Old 23rd September 2003, 11:59 PM   #8
diyAudio Member
 
purplepeople's Avatar
 
Join Date: Mar 2003
Location: London, Ontario, Canada
Kay: Is the pot parallel to the 1K resistor (ie. connected to ground)?

:)ensen.
__________________
Those who claim to be making history are often the same ones repeating it.
  Reply With Quote
Old 24th September 2003, 12:11 AM   #9
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Want to keep bias constant and stil have good control?

Use a contsant impedance series switched volume control.

Take it before I have it patented,
__________________
Frank
  Reply With Quote
Old 24th September 2003, 12:11 AM   #10
Banned
 
Join Date: Apr 2002
Location: Germany, Clausthal
why do you think the pot in the feedbacklopp should be lower quality than in the direkt signal? you need a good pot in both positions.

if you don´t like cheap pot in the signal path, there are many alternatives. A few:
http://home.arcor.de/dddddd-/index.html
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Volume control on DVD player remote. Lose resolution at low volume? Circlotron Digital Source 2 10th June 2011 07:20 PM
i need preamp schematics w/o tone control or volume control hernanstafe Parts 7 30th January 2008 03:12 AM
The remote control paratactic volume control audio-gd Solid State 33 7th June 2007 11:16 PM
Volume control : - pot' or pot' variable feedback resistor (gain) ? ash_dac Solid State 5 1st August 2006 05:07 AM
remote control motorised control for volume pot/knob CharlesY Parts 0 25th July 2005 11:12 AM


New To Site? Need Help?

All times are GMT. The time now is 01:44 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2